1. Technical Field
The present invention pertains to the field of telecommunications. More particularly, the present invention pertains to controlling power or other uplink resources of mobile stations, such as the modulation scheme and/or the channel coding used for communication with a radio access network.
2. Discussion of related art
The invention is relevant to EGPRS (enhanced general packet radio system) and EDGE (enhanced data rates for global evolution) in particular, but can be used in all FDMA (frequency division multiple access) based systems in which inter-cell and inter-sector interference affects network performance, such as e.g. 3.9G (3.9-generation) mobile telephone technology, i.e. a mobile phone technology based on 3G but with expanded capabilities approaching the capabilities provided by 4G.
As is commonly known, a cellular telephone network includes a radio access network having a number of wireless terminals, called base transceiver stations or Node Bs or having other designators depending on the kind of cellular system, all referred to here as base transceiver stations (BTSs). The cellular telephone network also includes a core network coupled to the radio access network and thus to the BTSs, but through an intermediate controller entity, called here a base controller station (BCS). Each BTS wirelessly couples to any user equipment (UE) wireless terminal in the area surrounding the BTS, such area being called here a cell. The BTS is said to serve the cell. Each cell can in turn be made up of several different sectors. Typically, any sector and any cell at least partially overlap with some other sector or cell. Thus, there can be inter-cell interference and also intra-cell or inter-sector interference.
The term UE or UE wireless terminal as used here is to be understood as synonymous with the term mobile station, and indicates any equipment including a mobile terminal enabling a user to wirelessly communicate with a radio access network of a cellular communication system/network.
Inter-cell/sector interference limits network performance in tight frequency reuse cellular networks. Power control (PC) is one mechanism to limit interference. In GSM (global system for mobile communication) networks, for example, circuit-switched (CS) speech and packet-switched (PS) services can be allocated to the same frequency resources. In such arrangements CS and PS services interfere with each other. As CS services typically have more strict quality criteria, CS service power control is usually not used to limit interference of the PS service by the CS service, but PS service power control can be used to limit interference caused by PS traffic.
Dual Symbol Rate (DSR) is a mechanism that has been proposed for improving the performance of uplink (a communication from a UE to a BTS, as opposed to downlink) in a GSM/EDGE network. DSR has been proposed in various 3GPP (3rd Generation Partnership Program) contributions. See for example GP-05261, Agenda Item 7.1.5.5, “Updates for Dual Symbol Rate Section of the Feasibility Study on Future GERAN Evolution,” (GERAN stands for GSM EDGE radio access networks), 3GPP TSG (Technical Specifications Group) GERAN#27, Atlanta, USA.
In DSR, to improve uplink in a GSM/EDGE network, the symbol rate is doubled and the transmitter signal is allowed to overlap adjacent carriers. DSR nearly doubles uplink data spectral efficiency and is, therefore, a significant uplink capacity enhancement feature for the EDGE evolution.
The DSR carrier, however, overlaps with three normal carriers so that usage of DSR significantly increases network interference. With tight frequency reuse, significant interference in uplink is received by a BTS not only from adjacent sectors but also from surrounding cells.
Receivers with interference rejection combining (IRC) algorithms can mitigate interference and so usage of IRC receivers improves performance in a case of use of DSR (or other mechanisms tending to significantly increase inter-cell and inter-sector interference).
In a GSM system, the currently specified EGPRS uplink power control algorithm is based on the serving cell signal level, and optionally also on various specified quality measurements. (Both open and closed loop algorithms have been presented.) However, when power adjustment is made based only on the signal level and the quality measurements, the amount of interference occurring in neighboring cells is not taken into account, whereas if it were, sometimes a mobile station would be able to use more power than the signal level and quality measurements would indicate, and sometimes should use less. For example, in case of a path loss based open loop power control algorithm, if two mobile stations have the same path loss to a serving BTS the algorithm would call for the same power for both, but from the point of view of interference to communications between other BTSs and the mobiles being served by them, one of the two mobile stations might be able use a higher Tx (transmit/transmission) power than the other without causing unacceptable interference to the neighboring cells.
In other words, the problem is that when power control is based only on measurements of signals communicated between a UE and its serving BTS—e.g. path loss and C/I (carrier to interference) estimation—and interference to other cells is not considered, then sometimes the Tx power for the UE is unnecessarily limited. This decreases system capacity.
It would be advantageous, therefore, especially e.g. in case of DSR in a tight frequency reuse network, to base power control for a UE not only on measurements of signals between the UE and its serving BTS, but also on whether an increase in power would or would not tend to unacceptably impair communication in surrounding cells, which would depend on the amount of interference already present in the surrounding cells.